Snippet to rotate around a globe in two axes

dual_rotation.cpp

/*
    RotationFromEulerAngles()

    This solves the issue where rotating on one axis and then by another causes
    the second rotation to get distorted.  Instead the rotation on both axes are
    performed at once.

    +yaw (radians) rotates the camera clockwise.
    +pitch (radians) rotates the camera so it is looking slant-downward.

    Coordinate system used by mesh:
    (+x, +y, +z) = (+right, +down, +forward)
*/
static Quat RotationFromEulerAngles(float yaw, float pitch)
{
    /*
        Math review:

        Quaternion from axis-angle:
            qx = ax * sin(angle / 2)
            qy = ay * sin(angle / 2)
            qz = az * sin(angle / 2)
            qw = cos(angle / 2)

        cross(a, b) = |a|*|b|*sin(angle)*(normal vector to a, b)
        dot(a, b) = |a|*|b|*cos(angle)
    */

    // Signs and offsets are tuning to fix up the coordinate system
    yaw += M_PI_FLOAT;

    // Half angle for quaternion formula
    yaw *= 0.5f;
    pitch *= 0.5f;

    // Points on sphere chosen by yaw, pitch
    Vector3 p_f(cosf(yaw), 0.f, -sinf(yaw));
    Vector3 p_t(0.f, -cosf(pitch), -sinf(pitch));

    // Calculate cross- and dot-products for quaternion formula
    Vector3 c = cross(p_f, p_t);
    const float cos_angle = dot(p_f, p_t);

    return Quat(c.getX(), c.getY(), c.getZ(), cos_angle);
}

Based on https://github.com/glampert/vectormath